Rapid Wear-Underlying Belt Separation

Finding a rapid wear area in a tire that is in litigation usually leads to questions such as how long has this separation been in the tire and could the client have seen this a week or several weeks prior to the accident. What the tire looked like at some point prior to the accident is dependent on many factors (miles driven for one) and includes the background of the expert. Here is an explanation of rapid wear, its identification, and a brief description of meaning.

Rapid or accelerated wear is a localized worn area within the tread that is more worn than adjacent surrounding areas. While the outlying edges of the rapid wear area can be nearly any shape, it is most often circular or oval in nature. An exception to this shape rule is when the rapid wear is only in the shoulder and can be an inch or two wide by 360 degrees around the circumference. It is caused when the underlying belt structure becomes loose (i.e. a belt separation). When the rotating tire is not against the road surface, centrifugal force will pull this area slightly apart from the underlying belt or casing. On contact with the road surface there will be abnormal squirming of the tread, causing a higher abrasion in this area versus the areas with a tight belt structure.

Accelerated wear is not to be confused with irregular wear, which is generally much more wide spread in the tread pattern and not localized in nature. Also rapid wear will have a gradual approach and exit from/to the areas of "normal" tread wear, whereas irregular wear will generally not be gradual. Normal treadwear is whatever the tire miles per 32nd is in the part of the tire that does not have a loose belt structure. By gradual approach it is meant that the fastest wear rate will be the center or near center of the underlying loose belt structure. From that point as you move across the rapid wear area and approach any tight belt structure, the wear rate decreases. This gives a boundary of some gradualness to rapid wear rather than a very abrupt ending point.

When the rapid wear area is worn such that the siping in that area starts to disappear, the "disappearance" can be a complete elimination of the sipe, or the sipe will change in shape from those same sipes in another area of the tire. This is the clue that a depth change has occurred. That area becomes more visibly obvious, and will continue to become even more clearly visible with time, until either there is a tread/belt detachment or the area is finally observed and the tire removed from the vehicle.

Due to the various degrees of rapid wear, and the possible locations (outboard or inboard side on a vehicle), and the type of vehicle fender well area, rapid wear is at times either easy or very difficult to spot.

In passenger car tires rapid wear is most always caused by an underlying separation. There are times, specifically in heavy truck tires with very stiff tread / belt packages that rapid wear can be caused by overlapping components. By careful examination of any changes in the siping circumferentially or radially around the tire the forensic expert, in a laboratory environment, should be able to pick out rapid tread wear regardless of how subtle the area.

The amount of rapid wear present will depend on :

• The size of the underlying separation. The separation needs to reach a size such that the tread squirm in that area is sufficiently different than the surrounding area revealing itself in the worn appearance of the tread.
• The rapidity of the growth of the separation. A rapid wear area requires a "slow" growth to the separation so that with time the tread wear differences become visible. Rapid growth separations do not have the time necessary for rapid wear.
• The usage of the tire when the rapid wear begins ( i.e. load / speed / pressure).

To see the resume of the expert associated with this case study, see the link below.